As used herein and in the claims the "front part" of an airbag is understood to be the portion of the airbag that is presented for contact with a vehicle occupant when the airbag is inflated and deployed.
When deploying a passenger side airbag, a large volume of inflation gas (up to 130 liters) is delivered to the airbag in a relatively short time (about 25 milliseconds). This results in a risk of injury for the vehicle occupant, particularly if the vehicle occupant is out of position, for example when sleeping or leaning forward. Known sensing devices ensure that the airbag is deployed as a function of the unimpeded advance movement of the airbag which can be determined by the sensing device.